[hack] fix typo serializing additionalTextEdits
[hack] fix typo serializing additionalTextEdits

Summary: There's a simple typo here. The correct spelling is plural `additionalTextEdits`. We already use the correct spelling in this file when deserializing the structure. This diff just makes it serialize correctly outgoing.

Reviewed By: ATalaba

Differential Revision: D15714650

fbshipit-source-id: b898a1c75fe0ed6fa79d5b7f61503b5290a88dc0

gabelevi/flow,samwgoldman/flow,gabelevi/flow,gabelevi/flow,samwgoldman/flow,gabelevi/flow,samwgoldman/flow,samwgoldman/flow,facebook/flow,gabelevi/flow,mroch/flow,mroch/flow,facebook/flow,samwgoldman/flow,facebook/flow,gabelevi/flow,samwgoldman/flow,mroch/flow,facebook/flow,mroch/flow,samwgoldman/flow,mroch/flow,facebook/flow,facebook/flow,mroch/flow,mroch/flow,gabelevi/flow,facebook/flow